This invention is directed to a pin wheel feed mechanism suitable for use in a printer and like equipment, and, in particular, to a paper feed mechanism of the pin-feed type for transporting documents having perforations along the peripheral edges thereof.
Various constructions of pin-feed type paper transporting devices are known in the art. An example of such a device is described in U.S. Pat. No. 4,227,821 to Plaza et al. Although the drive mechanism disclosed in the Plaza et al. patent is alleged to be relatively simple in construction and low in cost compared with other pin-feed type devices, the paper transporting device of Plaza et al. is still complicated in construction and has a high manufacturing cost due to the fact that the mechanism disclosed therein requires a substantially large number of parts which in turn requires a complex assembly operation.
Additionally, although conventional pin-feed type paper transporting devices can operate reasonably well when the sheet or paper to be transported is sufficiently thin as compared with the height of the pins on the pin wheels which feed the paper through the device, the operation of these prior art devices becomes unreliable when a relatively thick sheet or a sheet having several layers of paper are to be transported through the mechanism. For example, many types of webs having perforations along their edges include an outer sheet and inner carbon sheets which allow printing on several pages at the same time. In this case, the engagement of the pins with the perforations on the periphery of the sheet becomes unreliable due to the presence of warps or bunched portions between adjacent pins where the several sheets of paper are joined together. This is particularly the case when the several sheets of joined paper move through the curved path defined by the surface of the pin wheel. These warps or bunches may cause the feeding paper to be pushed off of the pin wheel. Conventional pin wheels of the type discussed herein are disclosed in the Plaza et al. U.S. Pat. No. 4,227,821 and the Weller U.S. Pat. No. 4,022,365.
Accordingly, a pin feed mechanism which is simply constructed and inexpensive to manufacture with a concurrent reduction in the number of working parts which includes a pin wheel construction which avoids the disadvantages of the prior art pin wheels by making provision for warps in layered or thick feeding sheets, is desired.